The rabbit is a good animal model for the study of many human diseases because of its anatomical, genetic and biochemical similarities to the human. It is also used for drug screening, production of antibody and production of therapeutic proteins. The rabbit is large enough to provide adequate quantities of tissue for experimental work, produce sufficient amount of antibody or therapeutic proteins, and yet it is small enough to be economical for most laboratories. To date, pronuclear microinjection remains the primary method to produce transgenic rabbits. There are no germline competent rabbit embryonic stem (rbES) cell lines available. Pronuclear microinjection, however, is of low efficiency, results in random integration, and cannot produce gene targeted transgenic animals. The purpose of this SBIR project is to establish germline competent rbES cell lines for the production of gene targeted transgenic rabbits. In Phase I we propose to prepare rabbit embryonic fibroblasts as feeder layers, synthesize recombinant rabbit leukemia inhibitory (LIF) factor and derive putative rbES cells. We hypothesize that using feeder layers and LIF from rabbit origin will increase the chance of getting germline competent rbES cells. We expect to derive at least 20 putative rbES cell lines upon completion of the Phase I study. In Phase II, we will work to validate if these rbES cells can contribute to germ line cells after blastocyst injection and we will work to produce gene targeted transgenic rabbits from these cells. The success of this project will establish the first germline competent ES cell lines in a non-murine species, improve the transgenic efficiency in rabbits, and make the production of gene targeted rabbits possible. [unreadable] [unreadable] The rabbit is a good animal model for the study of many human diseases because of its anatomical, genetic and biochemical similarities to the human. It is also used for drug screening, production of antibody and production of therapeutic proteins. The main reason that rabbit has not been in these fields is that there have been no established germline competent rabbit embryonic stem (rbES) cell lines. The success of this project will establish the first germline competent ES cell lines in a non-murine species, improve the transgenic efficiency in rabbits, and make the production of gene targeted rabbits possible. [unreadable] [unreadable] [unreadable]